Further Reading

We rose before dawn and shuttled up the mountain to a frigid July sunrise overlooking the world. Waiting for us at the top were four all-electric prototype vehicles, camouflaged against unscrupulous photographers. They were new e-tron SUVs, outfitted for a European market but with aspirations of becoming Audi's American answer to Tesla's Model X. With 248.5 miles (400km) of range, a 95kWh battery, and dual-motor all-wheel drive, the car has the potential to be an electric all-terrain vehicle suitable for ski trips to Aspen.

As the sun inched its way up over Kansas, my fingers began to freeze. The 3:30am cup of coffee and the winding drive up the mountain and the thin, dry air all conspired to make me start feeling a bit sick. I hopped into one of these inscrutably decorated vehicles, hoping to take shelter from the high-altitude wind, and quickly noticed touch screens and paddle shifters and thin, not-yet-legal-in-America side-view cameras sticking out of the sides of the vehicle where mirrors ought to have been.

But the purpose of this drive was not to speculate on features, MSRP, and EPA fuel-equivalent numbers (all of that is still subject to change on the US version of the vehicle, which will likely be introduced in 2019). Instead, we were here to experience Audi's latest engineering developments: namely, the recuperation system that turns what would otherwise be kinetic energy, created during coasting and braking, into electrical energy. These features contribute to a full 30 percent of the prototype e-tron's range.

The rear of the prototype vehicle in the headlights of another one.

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Sunrise over Kansas.

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The front of Audi's prototype e-tron in the early dawn hours.

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Oh, there's dawn.

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The interior of Audi's prototype electric vehicle is screen-heavy.

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Audi engineers cooked up this app to show when and how the car's recuperation system would be kicking in. Such a graphic will likely not be available to regular customers, sadly.

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We stopped halfway down the mountain for a quick... brake. (I mean a break.)

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The vehicle is designed with aerodynamic concerns foremost.

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At the end of the drive, in the full, mid-morning sun, we look on the glory of the Garden of the Gods.

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Two braking systems

Regenerative braking and regenerative coasting are hardly new developments. But Audi's engineers have spent significant time optimizing the latter and getting it to work with the former in a way that maximizes recaptured energy and also offers a smooth drive.

Regenerative braking

Audi's e-tron SUV has two braking systems: an electronic braking system and a conventional, friction-based braking system. The electronic braking system usually responds when you're simply tapping the brakes: this initiates the regenerative braking system and captures that kinetic energy as electric energy.

However, if you apply more force to the brake, the brake control system knows you're trying to make a complete stop and initiates the standard hydraulic braking system. This hydraulic system won't capture any energy for you, but it will bring your vehicle to a complete stop.

The switch happens nearly instantaneously, and, in our test drive, it was imperceptible to me.

"The control unit detects with how much force the driver is depressing the brake pedal and calculates how much braking torque is needed within milliseconds," an Audi press release writes. "If the recuperation torque is not sufficient, a displacement piston in the brake hydraulics generates additional pressure."

When we were about halfway down the mountain, our driver, engineer Oswin Röder, pulled off the road to allow the passengers to stretch their legs and switch seats. A mandatory brake-check station awaited us, where a ranger usually uses a thermometer to see if you're at risk of burning out your brakes from all the downhill driving. Audi's prototype came in at a cool 48°F (9°C). Röder later invited us to touch the interior of the wheel on the brake rotor. I confirmed: all that kinetic energy that would have become heat had evidently become electric energy.

Regenerative coasting: Your car automatically knows how much to recuperate

Like with other battery electric vehicles, Audi's system can also recuperate energy as it coasts, drawing on the vehicle's two electric motors to create brake torque, which starts happening once you take your foot off the accelerator. You have a few options here, too. You can purely coast, which contributes nothing to regeneration. Or you can manually recuperate energy using the car's shift paddles, toggling between Level 1 and Level 2 settings, which adjust how much drag there is on the car's coast.

Further Reading

Additionally, you can set-it-and-forget-it with automatic coasting recuperation. This setting draws on the car's sensors, including a camera up front, to determine if you're coming up to a curve in the road or a wall of traffic on the highway. The system then adjusts the aggressiveness of the regenerative coasting accordingly. The slowing action of the brake torque on the electric motors creates what Audi calls a "one-pedal feeling," where you can slow the car without using the brake at all. That comes from Audi, of course: none of the journalists was allowed to drive the prototypes. We were just allowed to sit in them.

Audi says that, with coasting and braking combined, energy is usually being generated during 90 percent of all decelerations.

This appeared true in practice: before the drive, the Audi team cooked up a small app connected to the vehicle's internal recuperation system, which showed us in real time exactly when Röder was recuperating energy, whether from the lack of acceleration or from the brake, and when he was expending energy in drive or when he hit the hydraulic brakes.

By the end of our journey down the mountain, we had pumped roughly 11kWh back into the battery. An Audi press release says that its regenerative braking system can recuperate up to 220kW at a time if the driver applies the brakes when they're going roughly 60 miles per hour.

Throughout all this driving, the car is constantly calculating whether the front or the rear axle should be contributing to deceleration the most. Usually, the rear axle is the star of the show, but as the car takes a turn, it will intelligently move some regenerative drag torque to the front axle.

Of course, it's good to keep in mind that this is still just a prototype vehicle and a prototype vehicle with EU specs at that (the specs will inevitably change for the US market, notably those side-view mirrors, barring a stroke of good sense from the federal government).

A few notes about the rest of the car, which will likely change

Currently, replacing side-view mirrors with cameras is not street-legal, but Audi is hoping it will become legal in the US soon.

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The vehicle's brake rotor wasn't hot to the touch after a lot of downhill deceleration.

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The driver's side-view camera screen is touch-sensitive, allowing the driver to adjust either mirror intuitively.

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I just really like the view you get with these cameras.

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The drive last week was very focused: journalists did not get to drive the e-trons, and nearly every question about non-recuperation features on the car was met with the disclaimer that the answer is subject to change. More details will be available when the SUV is officially announced on September 17. Still, we can say that the aerodynamics of the car were a primary concern for Audi, to the point that these e-tron SUVs had specially designed wheels that streamlined the gap between the wheel and the rim and specially designed lettering, also for aerodynamic purposes.

The side-view cameras also caught everyone's eye. Although I used to be a skeptic about this, especially after reading Ars comments along the lines of "mirrors are a simple tool, impervious to hacking, that has worked for thousands of years!" I now disagree. On this e-tron, the cameras' fields of vision were elegantly shown in a small triangular space inside the side-view camera's door, and the image was way better than anything you'd get with a mirror. Removing side-view mirrors doesn't do much for aerodynamic effect at normal passenger vehicle speeds, but it does make highway driving quieter, and that's a laudable goal.

Plus, good old-fashioned mirrors can be "hacked," too: a friend of mine was in college when an unknown drunken reveller roundhouse-kicked the side-view mirror off the driver's side of her vehicle. It's a cruder crime than hacking a camera, but both are solved by making sure you look over your shoulder when you change lanes (like you should be doing anyway) on your way to the shop to get it fixed.

Although we were mostly cruising the winding road down the mountain slowly, we did get a moment on the highway as we returned to the hotel outside Colorado Springs. Here, Röder stepped on the gas, and like all good electric vehicles, the acceleration was instantaneous, and the ride was quieter than you'd find in a gas vehicle.

Finally, sitting inside the e-tron was very comfortable. The interior climate is augmented with a heat pump that allows the car to recuperate heat from the battery, yet another nod to the efficiency of this vehicle. Seats can be heated or cooled, and there was plenty of space in both the front and the back for my legs and my laptop bag. So, as a passenger, the drive was great. As a driver concerned about range and comfort, I'm sure it'll be even better.

93 Reader Comments

So, electric cars can use regenerative braking to charge the battery, and the Audi does this.

Further, if you start at the top of a mountain, and use regenerative braking on the way down, you end up with energy in the battery.

What's interesting here, in particular?

I'm more excited about the side view cameras. Which, certainly, can also be kicked off, but it would be a nice improvement over having to adjust the mirrors every time you switch drivers (as the camera positioning for an optimum view won't change if the driver head position changes).

I'm going to "speculate on the MSRP" and speculate that I'm unlikely to be affording this when it comes out, though.

Why is there so much in the write-up about regenerative braking? Doesn't every electric (and hybrid) car already have this? I don't understand who the target audience of this article is.. is it supposed to be an introduction to electric cars for someone who has never heard of them before? Perhaps that would be better as a standalone article instead of what seems like it should be a review of a specific vehicle.

Nothing here sounds any different than any other electric or hybrid car that's been using regenerative braking for ages.

What this describes is, as far as I can tell, exactly how the brakes in my Volt work.

I was going to say, Gen 1 Volt does practically all its "braking" with the electric motors. What exactly is so special about this system? If anything, it sounds less able than the Volt since it appears that it will blend the brakes in whenever you come to a full stop. The Volt only uses the friction brakes below 5 mph or in an emergency stop.

Yeah I don't get the article. Nothing new about regenerative breaking or coasting and other EVs already advertise the one pedal driving. Maybe they have some slightly new tweaks to the basic idea using extra sensors or took extra time to tune things for the particular case but how is that news worth?

How is this article not "Hey we made and EV that does standard EV stuff."

What's next an article about how an EV has a battery and an electric motor in it?

Seems like yet-another-concept car. The European manufacturers are very good at producing concept cars and have been for decades, but can they put a long-range BEV in production at a competitive price?

It's going on sale next year. The actual launch event when we find out all the specs/price/etc is next month. You're deluded if you think this is a concept car that will never see the light of day.

Quote:

If Tesla starts cherry-picking all the desirable customers from them, leaving just the customers who need heavily subsidized leases, how are companies such as Audi, BMW, Mercedes and Porsche going to find the funds to switch to BEV cars?

Have you actually looked at which cars people are trading in when they buy new Teslas? Its mainly Priuses, Civics, Accords, Leafs (Leaves?) and 3 Series.

If Tesla starts cherry-picking all the desirable customers from them, leaving just the customers who need heavily subsidized leases, how are companies such as Audi, BMW, Mercedes and Porsche going to find the funds to switch to BEV cars?

~88 million cars were sold worldwide in 2016.

That's roughly 1.7 million a week: 1,700,000

Tesla has just gotten Model 3 production to 5,000 per week, and is around 2,000 per week with the Model S/X lines.

That's 7,000 per week.

Versus a global sales of 1,700,000 per week.

I'm not worried about Tesla gutting the other automakers any time in the near future. Audi, BMW, Mercedes, and Porsche all produce far more than just top end luxury cars.

Nothing here sounds any different than any other electric or hybrid car that's been using regenerative braking for ages.

What this describes is, as far as I can tell, exactly how the brakes in my Volt work.

I was going to say, Gen 1 Volt does practically all its "braking" with the electric motors. What exactly is so special about this system? If anything, it sounds less able than the Volt since it appears that it will blend the brakes in whenever you come to a full stop. The Volt only uses the friction brakes below 5 mph or in an emergency stop.

And the Chevy Bolt will come to a complete stop without touching the brake peddle, even on a slight down slope. It will engage the parking brake if you have it configured to do so.

From reading the article the Audi is not truly a one pedal car as it stops regen at 5mph. I do realize that once you get to a certain point you are actually using more energy for brake torque than you are getting back in regen but at less than 5mph I'd rather not have to touch the brake peddle. I have really become accustomed to almost never needing it.

I've been driving an e-tron for a couple years now*. When I go down a mountain in Shenandoah, I get like a 3rd of the battery back. If I press hard on the brake, it brakes with regular discs. What is so new about this?

If the reader's not familiar with EVs the extensive description provides good information, but from an EV owner's view, e-tron's "recuperative system" is painfully run-of-the-mill, except for the part where the level of regenerative coasting is adjusted according to the environment.

As far as I can tell, true one-pedal driving is possible in Chevrolet Bolt EV but not most of the other EVs because Bolt EV continues regenerative braking all the way to a full stop, unlike others which stop around 5 to 8km/h. I think this is why e-tron was described as "one-pedal feeling". I've been driving Bolt EV for several months now and due to the one-pedal driving (L mode) the brake only gets used during emergency, i.e., the regenerative energy capture happens during 99+% of all decelerations.

So, electric cars can use regenerative braking to charge the battery, and the Audi does this.

Further, if you start at the top of a mountain, and use regenerative braking on the way down, you end up with energy in the battery.

What's interesting here, in particular?

I'm more excited about the side view cameras. Which, certainly, can also be kicked off, but it would be a nice improvement over having to adjust the mirrors every time you switch drivers (as the camera positioning for an optimum view won't change if the driver head position changes).

I'm going to "speculate on the MSRP" and speculate that I'm unlikely to be affording this when it comes out, though.

Yeah and I've driven antique Prius that have a "B" for regen braking setting in the gear shift. When I'm driving around town, I just leave it in "B" and the car aggressively regen brakes whenever I lift my foot off the gas. It works greatly for maximizing range. I don't understand what is different about this story and that antique Prius, except maybe it has some "whoop so what" digital features like scanning the road ahead to automatically set the regen braking levels?

Nothing here sounds any different than any other electric or hybrid car that's been using regenerative braking for ages.

What this describes is, as far as I can tell, exactly how the brakes in my Volt work.

I seem to remember GM marketing the EV1 as being the first with regenerative braking in 1996. The following year Toyota came out with the Prius which also had regenerative braking. So this indeed seems like the same technology we have had for two decades now.

Okay, I know it's a concept/test vehicle and all that, but I swear my first thought on looking at the picture was "I wonder what you would be buying if you ran that car through a department store scanner."

Sounds like an improvement in the efficiency of regenerative braking. Beyond that, not much new about that concept. Maybe new to Audi?

They are missing an opportunity here. If side mirrors are replaced with screens, make the camera basically flush with the car to reduce aerodynamic impact (minor) but make the thing less likely to get damaged. Side mirrors with tech in cost a lot to replace. Could be a wide angle lens almost flush with the bodywork.

Seems like yet-another-concept car. The European manufacturers are very good at producing concept cars and have been for decades, but can they put a long-range BEV in production at a competitive price?

If Tesla starts cherry-picking all the desirable customers from them, leaving just the customers who need heavily subsidized leases, how are companies such as Audi, BMW, Mercedes and Porsche going to find the funds to switch to BEV cars?

I'm sorry, but this is complete gibberish.

The iPace is slated for mass production, this SUV is slated for production with a formal announcement in about a month.

And what exactly do you consider a reasonable price? Even the Model 3 will set you back $50k. An Audi SUV? Target price is probably at least $80k - if it is sold in the US - BEV or not. I think they can post margins on par with the Model X at that price point...

WTF. What an article. I kept waiting for the interesting part, but it never came.

"Audi, like everybody else, are continuing their development of regenerative braking technology which, despite modest incremental improvements, has remained essentially unchanged since its introduction roughly two decades ago. I was allowed to sit in one of their cars. Also, cameras for mirrors."

On the efficiency front, it seems woefully lacking, despite all that talk about recuperating energy. All modern EVs get the stated range with the help of regenerative braking and energy management, and yet, according to the article, e-tron has a mere 400km range out of a 95kWh battery. Tesla Model X is listed as being able to travel 465km with a 100kWh battery. It's great that we're seeing some competition in the SUV space, but that's about it.

By the way, if you go down to the smaller cars you can get a 400km range out of a 60-ish kWh battery. Hyundai Kona Electric gets 405km with 64kWh; Kia Niro EV, 385km with the same capacity. Chevy Bolt EV does 383km with 60kWh. Tesla Model 3 is supposed to do 350km with 50kWh.

Nothing here sounds any different than any other electric or hybrid car that's been using regenerative braking for ages.

I've yet to drive in a car with regenerative braking but I've always wondered exactly how the mechanical side of it works, and if the system feels any different to the driver. While I guess the time will come when I get to find out for myself, what I valued most from the article was simply the line about the transition being "imperceptible".Friction brakes have obviously been around for longer than regenerative braking but I am still interested to know more about the engineering challenges of designing them and how (if) they "feel" to the driver.

Seems like yet-another-concept car. The European manufacturers are very good at producing concept cars and have been for decades, but can they put a long-range BEV in production at a competitive price?

It's going on sale next year. The actual launch event when we find out all the specs/price/etc is next month. You're deluded if you think this is a concept car that will never see the light of day.

Quote:

If Tesla starts cherry-picking all the desirable customers from them, leaving just the customers who need heavily subsidized leases, how are companies such as Audi, BMW, Mercedes and Porsche going to find the funds to switch to BEV cars?

Have you actually looked at which cars people are trading in when they buy new Teslas? Its mainly Priuses, Civics, Accords, Leafs (Leaves?) and 3 Series.

Can you address the oddness of the article and how it seems to assume the audience is unfamiliar with how an EV/hybrid works? This doesn't seem like the kind of article I'd expect to see on ars. Very remedial.

I've yet to drive in a car with regenerative braking but I've always wondered exactly how the mechanical side of it works, and if the system feels any different to the driver. While I guess the time will come when I get to find out for myself, what I valued most from the article was simply the line about the transition being "imperceptible".Friction brakes have obviously been around for longer than regenerative braking but I am still interested to know more about the engineering challenges of designing them and how (if) they "feel" to the driver.

My C-Max feels like I pushed it into second or third gear, depending on what speed I'm driving at when I lift from the accelerator.

Integrating data from the forward-facing sensors with yaw and acceleration data from the stability control to expand the envelope of effectiveness for the regen braking system seems like a notable advancement.

I was about to say the same thing. My 2018 Nissan Leaf does this, and the fantastic e-Pedel helps too. I have experimented when diving down steep hills and it uses regen braking, (and shows the energy being generated on a dial), but if I slam on the brakes to avoid something, the regular brakes kick in and nothing is show on regen dial.

Yes, all EVs have regen. What seems to have been missed by most is that according to the article this one does 220 kW of it! That is serious power, over double of what Tesla currently does on the 100 kWh packs. Perhaps the 800V architecture allows Audi to do that.

Yeah and I've driven antique Prius that have a "B" for regen braking setting in the gear shift. When I'm driving around town, I just leave it in "B" and the car aggressively regen brakes whenever I lift my foot off the gas. It works greatly for maximizing range. I don't understand what is different about this story and that antique Prius, except maybe it has some "whoop so what" digital features like scanning the road ahead to automatically set the regen braking levels?

unfortunately, this is not the right thing to do with a prius transaxle. B mode also causes the engine to absorb some of the energy and is converted to heat rather than electricity.

but the prius has such a small battery that it may not matter. you'll probably get enough energy regenerated anyway. at any rate, hypermiling in a prius is best done in D mode.

Would have preferred this article to be more about what makes Audi’s system different. Somewhere hidden in all the gushing seems to be that Audi has some optimizations that are more advanced than competitors. But from just reading the article, I couldn’t tell what might be a standard EV feature, what might be shared with only a few competitors, and what might be unique to Audi’s system.

My favorite example of regenerative braking is the dump trucks used in a cement quarry near Biel, Sitzerland. They go up the mountain empty, and come down full. They end up generating net power, so they occasionally stop to discharge their batteries into the grid.

I've yet to drive in a car with regenerative braking but I've always wondered exactly how the mechanical side of it works, and if the system feels any different to the driver. While I guess the time will come when I get to find out for myself, what I valued most from the article was simply the line about the transition being "imperceptible".Friction brakes have obviously been around for longer than regenerative braking but I am still interested to know more about the engineering challenges of designing them and how (if) they "feel" to the driver.

If you had only regen braking it would indeed feel very different, because the braking efficacy falls off as the vehicle speed drops. ie at very low speeds you get very little braking power, and at zero speed you get none! So a regen-only braking system would be unable to hold a car stationary on a hill, for example. That's why every EV that has regen braking still carries friction brakes.

There's some fairly difficult software involved in balancing the two systems so that it still feels like the braking in an IC car.

This technology is pretty well-established in other areas. Trains in New York City use it to feed power back into the system.

There was even a tram in Auckland, NZ in the 1950's that tried this. It couldn't be the last tram off the day on some lines, as the Mercury arc rectifiers couldn't work in reverse.

NYC subway never closes. There is no last train of the day.

I never realized how unique this was until I got stuck taking a rather expensive cab ride in London, after the Underground closed one night. Turns out the reason for this is not that somehow NYC is more of a 24-hour city. It’s that most of the NYC subway lines have separate express and local tracks. To do track repair/replacement/inspection, you can just shut down one of the tracks. Shut down a section of express track overnight, and it just means people take the local train. Shut down a section of local track overnight, and it just means running short-distance shuttle buses from the closed local stations to the nearest express station.

I've yet to drive in a car with regenerative braking but I've always wondered exactly how the mechanical side of it works, and if the system feels any different to the driver. While I guess the time will come when I get to find out for myself, what I valued most from the article was simply the line about the transition being "imperceptible".Friction brakes have obviously been around for longer than regenerative braking but I am still interested to know more about the engineering challenges of designing them and how (if) they "feel" to the driver.

If you had only regen braking it would indeed feel very different, because the braking efficacy falls off as the vehicle speed drops. ie at very low speeds you get very little braking power, and at zero speed you get none! So a regen-only braking system would be unable to hold a car stationary on a hill, for example. That's why every EV that has regen braking still carries friction brakes.

There's some fairly difficult software involved in balancing the two systems so that it still feels like the braking in an IC car.

The other reason to have friction brakes is that they are mechanically connected to the brake pedal and will work in the case of electronics failure. The issues you point out could, with some even more tricky software and the right kind of motor, be solved by using battery power to provide extra braking power at those lower speeds (energize the motor in such a way as to provide torque in the direction opposite of motion). But even then you’d want to have mechanically-connected friction brake backups.

This technology is pretty well-established in other areas. Trains in New York City use it to feed power back into the system.

There was even a tram in Auckland, NZ in the 1950's that tried this. It couldn't be the last tram off the day on some lines, as the Mercury arc rectifiers couldn't work in reverse.

NYC subway never closes. There is no last train of the day.

I never realized how unique this was until I got stuck taking a rather expensive cab ride in London, after the Underground closed one night. Turns out the reason for this is not that somehow NYC is more of a 24-hour city. It’s that most of the NYC subway lines have separate express and local tracks. To do track repair/replacement/inspection, you can just shut down one of the tracks. Shut down a section of express track overnight, and it just means people take the local train. Shut down a section of local track overnight, and it just means running short-distance shuttle buses from the closed local stations to the nearest express station.

Well, theoretically that's all true, but in reality sometimes pretty long stretches of subway line are shut down overnight or on a weekend to give crews a chance to chip away at decades' worth of backlogged maintenance. As impressive as our system is, it's showing its age lately.

Why does there need to be a switch? can't they both be used simultaneously. Granted the energy recuperated from a hydraulic break won't be much but it's still not worth completely disabling the system.